1. Technical Field
The invention concerns a method of producing melt-bonding wires containing at least one electrical conductor, wherein the at least one electrical conductor is provided with a layer of insulation covered by a meltable bonding layer, a device for producing melt-bonding wires containing at least one electrical conductor with a layer of insulation covered by a meltable bonding layer with a coating device for applying the bonding layer, as well as a melt-bonding wire with at least one electrical conductor surrounded by a layer of insulation covered by a meltable bonding layer.
2. Description of the Prior Art
Known melt-bonding wires have an electrical conductor with an electric insulation made of an insulating lacquer, which is provided with an additional bonding layer of a solvent-containing bonding lacquer. By means of this bonding layer, windings of melt-bonding wires bond after being sufficiently heated, for example by means of a pulsed current, by melting the bonding layers of the neighboring wire windings into a solid bonded connection.
Usually the bonding layer is produced by repeatedly applying and burning-in solvent-containing layers of lacquer. Depending on the viscosity of the lacquer needed for the coating process, liquid meltable bonding lacquers containing 65% to 90% of solvents are used for that purpose and therefore only contain 10 to 35% of solids. The burning-in of the bonding layer takes place in a separate oven, so that in addition to the oven required to burn-in the insulation lacquer, another oven is needed for burning-in the bonding lacquer. In both ovens, the film of insulating lacquer or the covering film of bonding lacquer are hardened by the effect of temperature which removes most of the solvents contained in the layers of lacquer. The released solvent vapors are routed to downstream catalyzers where they are burned.
The solvents contained in the lacquers being used are toxic as a rule, they produce intensive odors and are caustic. This applies in particular to the bonding lacquers containing 65% to 90% of solvents. The solvents being used are cresol, xylenol, NMP solvent, butanol and others. They form explosive mixtures during evaporation which must be controlled with a correspondingly expensive technology. In addition the solvents, which are unavoidably emitted by the lacquers used to apply the insulation and bonding layers, pollute the atmosphere and require costly ventilation equipment. Furthermore the vapors released into the atmosphere after the catalytic burnout contain residual amounts of toxic substances. Beyond that, residual amounts of solvents are released when the windings made of the known melt-bonding wires are heated, particularly when the windings are heated by means of pulsed currents to melt the bonding layers of neighboring wire windings.